Focal Adhesion Kinase (FAK) is an important survival molecule that is upregulated in a broad range of solid tumors and is expressed at very low levels in normal tissues, creating a therapeutic window and making this protein a highly attractive target for the treatment of cancer, as suggested by our lab [1] and recently by other leading authors in the field [2.3]. See also WO 2005/049852, the contents of which are incorporated by reference. We have identified the key-binding partners of FAK and peptides from the binding sites that cause apoptosis in cancer but not normal cells. Based on these findings as well as correlative structural and functional data, we suggest that blocking FAK-protein interactions will lead to apoptosis and tumor cell death. We have well-documented data that targeting FAK interactions is important for cell survival, and we have used atomic resolution structural data of specific binding sites to identify small molecule lead compounds. We have screened small molecule libraries and identified several lead compounds that disrupt binding of FAK to key signaling molecules and induce apoptosis in breast, colon, pancreatic, lung, as well as melanoma cancer cell lines. Some of these compounds caused apoptosis at low nanomolar concentrations. We also have shown that lead compounds increase the sensitivity of cancer cells to standard chemotherapy drugs.
Our data suggest that peptides and small molecule inhibitors of FAK can be identified as lead compounds to provide the basis for targeted novel cancer therapeutic agents. Such compounds will effectively reduce activation of both molecules involved in survival signaling and will lead to cancer cell death and sensitivity to chemotherapy. We anticipate that our approach (targeting FAK protein-protein interactions) is amenable to more successful drug discovery and development than the typical method of targeting the kinase activity by targeting ATP binding site of tyrosine kinases. Experience shows that it is especially difficult in the case of FAK, as several large pharmaceutical companies have failed to develop specific inhibitors of FAK that target kinase activity due to cross-reactivity with other essential tyrosine kinases.
The market for novel drug therapy targeting cancers of the breast, colon, pancreas, and thyroid is extensive. According to the American Cancer Society, it is estimated that 425,000 new cases of these cancers will be diagnosed this year in this country alone. Cancer drug therapy is an existing major product line of several pharmaceutical companies, and the development of drugs targeting FAK would be a natural complement to their existing products.
FAK is overexpressed in many cancer types compared to other kinase targets. Compounds that target FAK could be prescribed for many cancer types including breast, colon, pancreas, thyroid, lung, and melanoma.
Several groups are exploring the targeting of FAK as potential cancer therapeutics. The targeting of FAK typically has been focused on the kinase domain of FAK. This approach has proven unsuccessful as disruption of the kinase domain does not specifically interfere with the signaling downstream of FAK and other related tyrosine kinases have been affected by the drugs. Delineated herein is a novel approach that investigates the protein-protein interactions that are very specific for downstream signaling of FAK. Furthermore, targeting different binding partners of FAK might be relevant to different types of tumors.
Our laboratory was the first to clone human Focal Adhesion Kinase in 1993 and demonstrate its upregulation in different human tumors [4.5]. Based on knowledge of FAK biology in normal and tumor cells, we have identified the protein-protein interactions of FAK as targets for small-molecule-based tumor therapy. Phage display analyses revealed many potential FAK binding partners, some of which we already discovered by different approaches (e.g., p53) [6] and some we characterized based on phage display data (e.g., VEGFR3) [7]. Many of the selected peptides caused loss of viability and apoptosis in cancer but not in normal cells in vitro. These results suggest that it may occur by mimicking binding sites for key partners of FAK. We are focusing on three key structural interactions of FAK and specific binding sites. The advantage of our approach is twofold: we have well-defined data that targeting FAK interactions is important for cell survival, and we have used atomic resolution structural data of specific binding sites to identify small molecule lead compounds[8-10]. We are utilizing these data for structural analyses of FAK binding to these small molecules. We have also developed a novel computational technique that can be applied to a wide variety of biomedically relevant target proteins [11, 12]. This method, called NCIDOCK, utilizes the atomic coordinates for the target protein as the basis for large-scale molecular docking experiments in which approximately 140,000 small molecules are positioned into specific structural features. Each compound is scored for its estimated binding energy to the target, and then ranked to generate a list of candidate lead compounds. We then request the top-ranked small molecules for functional testing.
We have performed preliminary screening of a chemical library of 240,000 such compounds for each of three selected binding sites of key partners of FAK and identified a series of small molecules that we have evaluated for inhibition of FAK function, followed by application of our extensive experience in FAK biology and our already evaluated model systems to perform multiple cell-based assays (viability, proliferation, motility and invasion, cell cycle and apoptosis) for the analysis of biological activity of the lead compounds. We examined cancer cell lines (e.g., breast, colon, pancreatic, lung, or melanoma human) with these selected FAK inhibitors and have reproducibly shown a significant decrease of tumor cell viability and increase in tumor cell death in vitro.